Final Exam

• Luquillo rainforest - Puerto Rico study

  • Catch rate and biomass declined by 2.2-2.7% annually
• Reports of insect declines from around the world
• Factors that may be causing the insect apocalypse

  • Temperature changes
  • CO2 changes
  • Water availability changes
  • Invasive species
  • Habitat loss and degradation
  • Agricultural intensification
  • Urbanization/sub-urbanization
  • Light/chemical pollution
  • A mix of factors
• How insects deal with adverse conditions

  1. Wait it out (diapause - delayed development in response to recurring adverse conditions)

  2. Escape (quiescence - delayed development in direct response to adverse conditions)

  3. Migration/dispersal (tracking suitable environments/resources)
• What is changing that may be causing the insect apocalypse
• How do insects deal with adverse conditions?


  • wait it out
  • escape
  • diapause
  • quiescence
  • dispersal/migration
• Diapause


  Period of delayed development (dormancy) in response to recurring periods of adverse environmental conditions; development resumes in response to specific stimuli (i.e., photoperiod)
• Quiescence


  Period of delayed development (dormancy) in direct response to adverse environmental conditions; development resumes once favorable conditions return
• temperature change is one of the most important environmental stressors for insects
• Poikilothermic


  (adj. poikilothermic) the inability to maintain an invariant body temperature independent of the ambient temperature
• Ectothermy


  (adj. ectothermic) the inability to regulate the body temperature relative to the surrounding environment
• As things heat up

  • Faster generation times
  • Higher survival (escape from enemies)
  • Lower survival (if already at limit)
• Higher survivorship (less death) during diapause


  Less snow cover = no thermal protection
• Timing conflict with fixed cues to end diapause


  Potential consequences of milder winters
• Climate change is predicted to increase losses due to insects
• Increase of 2°C temperature


  Can create mismatches among organisms: physiological tolerances determine response to temperature changes
• Insect activity


  Can become mismatched with host plants or prey or other interactors
• Butterflies and moths in western Europe expand their northern range, but not their southern range
• Elevated CO2


  Currano et al 2008 found more insect herbivory during the Paleocene-Eocene Thermal Maximum (PETM), an abrupt global warming event 56 mya linked to transient increases in atmospheric CO2
• Studying effects using FACE

  free-air carbon dioxide enrichment
• General plant responses to elevated CO2

  • ↑ photosynthetic C fixation
  • ↑ plant growth rate
  • ↓ % nitrogen in leaves ('nitrogen dilution effect')
  • ~15% decrease in foliar N
  • ↑ carbon-based insect defences (e.g., tannins)
• General insect responses to elevated CO2

  • Insects ate more food (↑ per capita leaf area consumption)
  • More vulnerable to enemies (↑ mortality from natural enemies, e.g., parasites & predators)
• No evidence that compensatory feeding was due to leaf nitrogen content not being affected by CO2, but sugar concentration was higher (sugar = phagostimulant for Japanese beetles)
• Insect responses to elevated CO2

  • Abundance
  • Survival
  • Development time
  • Pupal weight
  • Conversion efficiency
  • Relative consumption rate
  • Relative growth rate
• There are fewer total insects, and a trend towards lower survivorship. Longer development time and lower pupal weight are indications of poor performance. Indications of poor-quality food: insects are eating a lot of food, but not doing a good job of converting that food into growth.
• Relative humidity


  Direct effects on insects
• Water limitation


  • ↓ plant growth rate
  • ↑ free amino acids (nitrogen)
  • ↑ plant chemical defenses (e.g., toxins)
  • ↓ plant physical defenses (e.g., resin)
• How does plant water stress free up amino acids?

  1. Protein synthesis and amino acid synthesis impaired

  2. Low osmotic pressure

  3. Existing proteins hydrolyzed, resulting in increased levels of free amino acids

  4. Accumulation of nitrogen-containing compounds to change concentration gradient (e.g., the amino acid proline)

  5. More nitrogen for insects!
• The main hormone controlling the drought response (ABA)


  Interacts with hormones controlling insect defense (SA & JA)
• Growth:


  • control
  • low
  • med
  • high
• Nutrient content:


  • control
  • low
  • med
  • high
• Dendroctonus ponderosae


  • A native beetle destroying western US forests
  • Climate change-mediated water stress inducing beetle outbreaks
  • Host plants: Pinus sp. (ponderosa & lodgepole pine)
  • Healthy conifers "pitch out" beetles with pressurized resin canals
• Psyllid outbreaks on Eucalyptus


  Correlate with drought stress
• Cabbage aphids feeding on collards

  • Increasing plant water stress (less water) = More aphids with less water
• leafhoppers in California vineyards


  • Prefer vigorously growing plants
• Insect responses to drought

  Vary because they respond to different plant traits
• Scientists need data and the community has eyes… and cars
• Pest


  An organism that reduces the quantity/quality/value/availability of some human resource
• Pest


  • Human-centered
  • Context-dependent
• Multicolored Asian Lady Beetle (Harmonia axyridis)


  • Feeds on aphids and other soft-bodied insects
  • Clusters around buildings
  • Reflex bleeding
  • Bite
  • Allergic reactions